A recruiter contacted me from their database. I can't say when they had my resume, as it was dated. I was passed around to multiple recruiters, and each one stopped the process at the telephone/coding stage.

I wouldn't share the question since I did accept their confidentiality agreement. But let me say, I was asked to solve a problem that, in its crude implementation, would yield O(n^2). The interviewer accepted it as a fair solution but wanted to know how I could convert that to O(1). I did. This was based on a reasonably well-known solution that is pretty similar to an LRU Cache, which you can look up on the internet. I emphasized how the solution is O(1).

Now, you can have a difference of opinion, but to rule that solution out and provide negative feedback to the recruiter, without opening your mind to other possible solutions or my past experiences and potential to think out of the box (even if you think that wasn't in your line of thinking and hence not an acceptable solution), shame on you.

You are Apple, and you supposedly think out of the box. Terribly disappointed.

That round should have easily taken me to a campus interview, but it didn't happen.